The pharynx is a passageway located within the neck and is part of both the respiratory and digestive systems since it serves as a conduit for both air and food. Anatomically, the pharynx is divided into three parts – the nasopharynx, oropharynx and hypopharynx – from above downwards.
The pharynx connects the nasal and oral cavities above with the trachea (or the wind pipe) and the esophagus (or the food pipe) below. Although the main function of the pharynx is to ensure that food and air are directed into their respective pathways, all three subdivisions comprise many structures with varied functions. Let’s take a look at each of them.
Nasopharynx – Uppermost Division of the Pharynx
The nasopharynx is the part of the pharynx located behind the nose. Air inhaled through the nose crosses the nasopharynx on its way into the trachea.
Structures in the nasopharynx include:
- openings of the Eustachian tubes – these are tubes connecting the ear cavities with the pharynx. Their purpose is to ventilate the middle ear and equalize middle ear pressure with atmospheric pressure for optimal hearing.
- fossa of rosenmuller – This is a small but deep cavern, often the starting point for cancer in these parts.
- adenoids – a collection of lymphoid tissue located in the roof of the nasopharynx. It is part of the immune system and helps protect the body from infective organisms. Adenoids are usually only present in children. They regress in size and gradually disappear as the child grows older.
- tubal tonsils – also lymphoid tissue, located around the Eustachian tube openings.
Oropharynx – Middle Part of the Pharynx
This is the part of the pharynx located behind the oral cavity. Air inhaled through the nose or the mouth travels through the oropharynx on its way into the trachea. Food swallowed passes through the oropharynx to reach the esophagus.
Structures in the oropharynx include:
- soft palate – this structure actually marks the boundary between the nasopharynx and oropharynx. When food swallowed is pushed into the oropharynx by the tongue, the soft palate immediately stretches to touch the pharyngeal wall, completely sealing off the oropharynx from the nasopharynx, preventing food from regurgitating into the nose and instead directing it down towards the esophagus.
- tonsils – these are lymphoid structures located on either side of the entry to the oropharynx from the oral cavity. These are the structures removed when a person undergoes tonsillectomy.
- base of the tongue – one-third of the tongue is actually fixed and located in the oropharynx.
- pharyngeal band – small nodules of lymphoid tissue scattered along the posterior pharyngeal wall.
Hypopharynx – Third Division of the Pharynx
This is the part of the pharynx situated behind the larynx or the voice box located at the upper end of the trachea. Food from the oropharynx passes through the hypopharynx to enter the esophagus as does air on its way to the trachea.
Anatomically, the hypopharynx is divided into three parts namely pyriform fossae, postcricoid region and posterior pharyngeal wall. Pyriform fossae are smooth depressions on either side of the larynx, acting as passages that guide swallowed food into the esophagus avoiding the larynx. The postcricoid region is the part of the hypopharynx directly behind the cricoid cartilage, one of the laryngeal cartilages. Cancers often occur in the hypopharynx.
Functions of the Pharynx
The main function of the pharynx is to act as a channel for food and air, directing each to its respective destination. Peristaltic or propulsive waves in the pharynx during deglutition or swallowing help drive food into the esophagus. It is very important that food be prevented from entering the trachea as anything other than air entering this passage into the lungs can result in dangerous aspiration or choking.
The lymphoid structures in the pharynx play a role in immunity. Together with the adenoids, tubal tonsils and the pharyngeal band, the tonsils form what is called the Waldeyer’s ring, a ring of protection around the nose and mouth, common portals of entry for infection. The pharynx also provides resonance to voice.
The pharynx, divided into three parts namely the nasopharynx, oropharynx and hypopharynx, acts as a passage for both air and food and plays an important role in respiration, deglutition and immunity.
Sources:
Gleeson, Michael J. "Scott-Brown's Otorhinolaryngology: Head and Neck Surgery" (Oxford University Press; 7 Edition, 2008)
Lakshmi Ananth - Lakshmi Ananth is a practising ENT, head and neck surgeon and has faculty position at a medical college. She is specially interested in ...
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